A seller on eBay is selling a lot of very rare Bella Sara promo cards from series like Best of Bella Sara (link) and very cheap lots of unopened card packs (link).
He's also selling cards which were only given out at special events like this Halloween set!.
There are even sealed boxes of cards that were never seen in stores such as Herds from the North of North (link). He also has miniatures, binders, and chibis for sale!